import java.util.Scanner;

public class 翻硬币 {
    static int N = 110;
    static char[] a = new char[N];
    static char[] b = new char[N];
    public static void main(String[] args) {
        Scanner s = new Scanner(System.in);
        a = s.nextLine().toCharArray();
        b = s.nextLine().toCharArray();
       int count=0;
       for(int i=0;i<a.length;i++) {
               if(a[i]!=b[i]) {
                   change(i,i+1);
                   count++;
               }
       }
        System.out.println(count);

    }
    private static void change(int x,int y) {
        for(int i=x;i<=y;i++) {
            if(a[i]=='*') a[i]='o';
            else a[i]='*';
        }
    }

}
